Back again. It's an interesting thread.
Brian -- I did point out that supernatural elements get lost on both sides of the Atlantic in time. From an early post:
"...Demons and dead lovers became ordinary murderers on both sides of the Atlantic, in time, of course."
Also from an early post of mine:
"'The Ballad Tree' by Evelyn Kendrick Wells. Published in 1950."
This is an excellent and readable book on this subject. Can't hurt to repeat this here.

I'd like to add "Let's go a-huntin'"/"Billy Barlow" to the discussion. Wren Hunting songs from the British Isles, like for example "The Cutty Wren", became a simple rat-hunting song in North America. (Of course nobody knows for sure where the change was made.
Cheers, Joy